Precision treatment of solid and liquid materials can be accomplished by heating the materials to a desired temperature at a location where treatment is desired. Examples of such heat treatment are soldering metallic parts, curing epoxy resins, removing plastic coatings from metals, and boring holes in solid materials.
Several techniques are currently used to perform precision heat treatment. One type of technique is optical, using focused light. This method is particularly preferred when the area to be treated is small (for example, less than 1 mm.sup.2).
Presented below are examples of some basic optical material treatment systems. The first of these is an optical soldering system. In this method, a tungsten xenon lamp is used as a light-emitting heat source. Fiber bundles transmit the emitted light to the material to be treated.
The drawbacks inherent in the use of optical soldering systems include large physical size of the apparatus, large power consumption and energy loss, large heat generation, high maintenance cost because of the short useful life of tungsten xenon lamps, and relatively large size of the operative focused light spot (typically approximately 1-5 mm diameter). The large light spot renders small component soldering difficult, and may cause damage to the substrate of the material being treated due to over exposure. In addition, these systems lack an efficient inspection system to check the results of the treatment. Inspection of the treated material is primarily accomplished with a camera or through careful examination by experienced inspectors.
Another technique is solid state laser soldering. The heat source in this case is a solid state laser, typically a neodymium activated yttrium aluminum garnet (Nd:YAG) laser. Problems such as large size, excessive power consumption, energy loss, heat generation (requiring a large-scale cooling system), high maintenance costs, and lack of efficient inspection capabilities are also inherent in this technique. In addition, speckle problems are encountered in homogeneous soldering operations.
Still another technique is gas laser soldering. With this technique, a gas laser, typically a CO.sub.2 laser, acts as the heat source. Large size, excessive power consumption, energy loss, heat generation, damage to nonmetallic substrate materials, and lack of efficient inspection capabilities are also inherent in this technique.
Finally, semiconductor laser soldering techniques exist. Here, a number of semiconductor diode lasers, typically III-V compound semiconductor diode lasers, are used as the heat source. This technique is particularly advantageous over the others because it solves many of the problems mentioned above, with the important exception of providing an efficient means to inspect the material after thermal treatment.
One such semiconductor diode laser soldering system is disclosed in U.S. Pat. No. 4,963,714 to Adamski et al. In that patent, a plurality of laser diodes are provided for generating a plurality of laser beams. Coupled to each laser diode is a fiber optic cable having a fiber optic strand therein that transmits the light generated by the diode. The fiber optic strands within each cable are brought together to form a single fiber optic bundle. A homogenizer is provided at the output end of the fiber optic strand bundle for converting the plurality of transmitted light outputs into a single high intensity laser beam. This laser beam is focused onto a spot on a printed circuit board where integrated circuit packages are to be connected.
In an alternative embodiment disclosed in the Adamski patent, a plurality of fiber bundles can be used to produce a plurality of high intensity laser beams simultaneously focused on the circuit board to facilitate the soldering of multiple locations concurrently, thereby reducing treatment time. Each laser diode in this apparatus has a power supply adapted to be selectively turned on and off, thereby controlling operational power to the diodes.
A laser soldering system providing some control of the laser beam is disclosed in U.S. Pat. No. 5,122,635 to Knodler et al. In this reference, a laser soldering system is provided wherein the power of the laser source and the vertical positioning of the laser are adjustable. The laser in this case is a CW-Nd:YAG laser. In one embodiment disclosed in the Knodler patent, a coupled vision system or image analysis system known in the art is mentioned for facilitating the positional assignment of the laser source.
In U.S. Pat. No. 5,023,426 to Prokosch et al., first, second, and third pattern recognition means using video cameras provide feedback to a controller. The controller manipulates a robotic arm and a staging unit to adjust the position of a circuit board under a laser beam.
U.S. Pat. Nos. 3,803,413 to Vanzetti et al., 4,481,418 to Vanzetti et al., and 4,657,169 to Dostoomian et al. disclose material inspection systems that detect infrared radiation from the material. The detected radiation values are compared to standards to yield information about the material. In the Dostoomian reference, the radiation values are used to determine the phase of solder in a reflow soldering operation. This information is then used to manipulate the soldering process.